Understanding mechanisms of reactions on catalysts requires the nature of active sites of the catalyst and the dynamic processes of the reactions to be understood starting when reactants enter the reaction zone, reaction intermediates begin to form, until final eluted reaction products exit the catalyst reaction system. For reactions involving simple species, in-situ techniques such as UV-visible and IR spectroscopies are typically used to probe the intermediates adsorbed on the catalyst. However, for reactions such as selective oxidations of organics, where reaction products and intermediates are complex, a single spectroscopic tool is insufficient. High resolution magic angle spinning (MAS) nuclear magnetic resonance (NMR) is a powerful and versatile technique for studying molecular structures and reaction dynamics regardless of whether the system under investigation is a solid, semi-solid, or a heterogeneous system containing mixtures of e.g., solid, semi-solid, liquid, and gaseous phases. While a number of in situ MAS NMR techniques have been developed to study heterogeneous catalysts, MAS investigations of catalyst reactions in situ have not yet been reported for MAS rotors with diameters larger than 7.5 mm due to technical challenges associated with sensitive detection of reactions occurring in shallow layers of catalyst beds placed in large bed volumes. The present invention addresses these needs. Additional advantages and novel features of the present invention will be set forth as follows and will be readily apparent from the descriptions and demonstrations set forth herein. Accordingly, the following descriptions of the present invention should be seen as illustrative of the invention and not as limiting in any way.